Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Statements of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Condensed Income Statements, Captions [Line Items]
Operating revenues, net	$ 216,294		$ 200,762		$ 625,510		$ 575,273
Expenses:
Direct expenses	170,531		160,731		499,541		468,428
Selling, general and administrative expenses	10,903		9,785		31,891		28,075
Management fees
Total operating expenses	181,434		170,516		531,432		496,503
Loss (gain) on disposal of assets, net	56		(1,399)		1,371		(16,075)
Impairment of assets							421
Equity in (income) loss of unconsolidated affiliate	(319)		(172)		(213)		911
Operating income	35,123		31,817		92,920		93,513
Equity in net income of consolidated subsidiaries
Interest expense	7,084		7,768		22,121		22,434
Loss on debt extinguishment					29,833
Other income, net	(238)		(163)		(498)		(388)
Total expenses	6,846		7,605		51,456		22,046
Earnings before income taxes	28,277		24,212		41,464		71,467
Income tax expense	11,028		10,435		16,168		29,336
Net earnings	17,249		13,777		25,296		42,131
Parent Company Only (issuer) [Member]
Condensed Income Statements, Captions [Line Items]
Operating revenues, net	128,580		125,160		375,326		354,453
Expenses:
Direct expenses	105,327		98,669		304,668		285,661
Selling, general and administrative expenses	8,597		7,365		24,307		21,719
Management fees			(3,024)				(8,833)
Total operating expenses	113,924		103,010		328,975		298,547
Loss (gain) on disposal of assets, net	56		(1,380)		1,371		(16,056)
Impairment of assets
Equity in (income) loss of unconsolidated affiliate	(319)		(172)		(213)		911
Operating income	14,919		23,702		45,193		71,051
Equity in net income of consolidated subsidiaries	(12,333)		(4,787)		(29,118)		(13,395)
Interest expense	7,082		7,631		22,119		22,297
Loss on debt extinguishment					29,833
Other income, net	(226)		(163)		(495)		(388)
Total expenses	(5,477)		2,681		22,339		8,514
Earnings before income taxes	20,396		21,021		22,854		62,537
Income tax expense	3,147		7,244		(2,442)		20,406
Net earnings	17,249		13,777		25,296		42,131
Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Operating revenues, net	87,714	[1]	75,602	[1]	250,184	[1]	220,820	[1]
Expenses:
Direct expenses	65,208	[1]	62,062	[1]	194,886	[1]	182,767	[1]
Selling, general and administrative expenses	2,306	[1]	2,420	[1]	7,584	[1]	6,356	[1]
Management fees			3,024	[1]			8,833	[1]
Total operating expenses	67,514	[1]	67,506	[1]	202,470	[1]	197,956	[1]
Loss (gain) on disposal of assets, net		[1]	(19)	[1]		[1]	(19)	[1]
Impairment of assets							421	[1]
Equity in (income) loss of unconsolidated affiliate		[1]				[1]		[1]
Operating income	20,200	[1]	8,115	[1]	47,714	[1]	22,462	[1]
Equity in net income of consolidated subsidiaries		[1]				[1]		[1]
Interest expense	2	[1]	137	[1]	2	[1]	137	[1]
Loss on debt extinguishment						[1]
Other income, net	(16)	[1]		[1]	(16)	[1]		[1]
Total expenses	(14)	[1]	137	[1]	(14)	[1]	137	[1]
Earnings before income taxes	20,214	[1]	7,978	[1]	47,728	[1]	22,325	[1]
Income tax expense	7,881	[1]	3,191	[1]	18,610	[1]	8,930	[1]
Net earnings	12,333	[1]	4,787	[1]	29,118	[1]	13,395	[1]
Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Operating revenues, net
Expenses:
Direct expenses	(4)				(13)
Selling, general and administrative expenses
Management fees
Total operating expenses	(4)				(13)
Loss (gain) on disposal of assets, net
Impairment of assets
Equity in (income) loss of unconsolidated affiliate
Operating income	4				13
Equity in net income of consolidated subsidiaries	12,333		4,787		29,118		13,395
Interest expense
Loss on debt extinguishment
Other income, net	4				13
Total expenses	12,337		4,787		29,131		13,395
Earnings before income taxes	(12,333)		(4,787)		(29,118)		(13,395)
Income tax expense
Net earnings	$ (12,333)		$ (4,787)		$ (29,118)		$ (13,395)

[1] Foreign subsidiaries represent minor subsidiaries and are included in the guarantors' subsidiaries amounts.